Substituted polyacetylenes are known, and although they have many possible uses, they are of particular interest for use in the fabrication of membranes for gas and vapor separations. Substituted polyacetylenes are particularly noted for their high gas permeabilities. In fact, the oxygen permeability of the substituted homopolymeric polyacetylene poly(1-trimethylsilyl)propyne [PTMSP], is the highest of any known polymer. Masuda et al., 105 JACS 7473 (1983). Although polyacetylenes substituted by bulky groups such as trimethylsilyl have extremely high permeability, their utility as membrane materials has been limited by their relatively low selectivities. For example, the selectivity of PTMSP toward oxygen over nitrogen (.alpha.O.sub.2 N.sub.2) is only 1.7 (a minimum oxygen to nitrogen selectivity of 4 is generally considered necessary to be commercially useful).
A few substituted homopolymeric polyacetylenes have been reported to have somewhat higher selectivities. For example, Masuda et al., in 29 Polymer 2041 (1988), report several aryl-substituted polyacetylenes with moderate oxygen to nitrogen selectivities. These include: poly(1-phenylpropyne) (.alpha.O.sub.2 /N.sub.2 =2.7); poly(1-phenyloctyne) (.alpha.O.sub.2 /N.sub.2 =2.5); poly (1-chloro-2-phenylacetylene) (.alpha.O.sub.2 /N.sub.2 =2.7); and poly(3-propyl, 3-(dimethyphenylsilyl)propyne) (.alpha.O.sub.2 /N.sub.2 =3.8). However, the last-mentioned substituted polyacetylene has an oxygen permeability of less than 10 Barrers.
What has been needed are substituted polyacetylenes that have both moderate to high oxygen to nitrogen selectivity (.gtoreq.4) and high oxygen permeability (.gtoreq.20 Barrers). One unsuccessful approach to achieving such a combination of properties in a single polymer is reported by Hamano et al., in 26 J. Appl. Polym. Sci.: Part A: Polymer Chemistry 2603 (1988), wherein the copolymerization of 1-phenylpropyne with 1-trimethylsilylpropyne [TMSP] is reported. Five polymers are reported having varying contents of trimethylsilyl repeat groups and the following permeabilities and selectivities:
0% TMSP: P.sub.O2 =10 Barrer; .alpha..sub.O2/N2 =3.0 PA1 25% TMSP: P.sub.O2 =40 Barrer; .alpha..sub.O2/N2 =2.8 PA1 50% TMSP: P.sub.O2 =400 Barrer; .alpha..sub.O2/N2 =2.3 PA1 75% TMSP: P.sub.O2 =1700 Barrer; .alpha..sub.O2/N2 =2.0 PA1 100% TMSP: P.sub.O2 =6000 Barrer; .alpha..sub.O2/N2 =1.7
There is therefore still a need in the art for a class of acetylenic polymers possessing both reasonably high selectivities and high permeabilities. This need is filled by the present invention, which is summarized and described in detail below.